Fully Nonadiabatic Analysis of Vibrational Instability of Population III Stars due to the ε\varepsilon-Mechanism

A linear nonadiabatic analysis of the vibrational stability of population III main-sequence stars was carried out. It was demonstrated that, in the case of massive stars with M \gtrsim 5\Mo, helium burning (triple alpha reaction) starts during the main-sequence stage and produces $^{12}{\rm C}$, leading to the activation of a part of the CNO-cycle. It was found that, despite of that, those stars with M\lesssim 13\Mo become unstable against the dipole g$_1$- and g$_2$-modes due to the $\varepsilon$-mechanism, during the early evolutionary phase at which the pp-chain is still the dominant nuclear energy source. The instability due to the $\varepsilon$-mechanism occurs against g-modes having a large amplitude in the off-centered $^3$He accumulation shell in the deep interior, and the growth time is much shorter than the evolutionary timescale. This instability is therefore likely to induce mixing in the stellar interior, and have a significant influence on the evolution of these stars.Comment: PASJ, 64, 2 (2012) in press. 9 pages, 8 figure

Solar Models with Helioseismic Constraints and the Solar Neutrino Problem

Imposing a constraint of the sound-speed profile determined from helioseismology and updating the microphysics, we have revised our seismic solar model, constructed with the assumption of a homogeneous metal abundance distribution, and have shown that the theoretically expected neutrino fluxes are still significantly more than the observations. With the same sound-speed profile constraint, we also constructed solar models with low metal abundance in the core, and evaluated the neutrino fluxes of these models to see if nonstandard solar models with a low metal core can solve the solar neutrino problem. Some of these models are in agreement with the Homestake data, the Super-Kamiokande data, and the sound-speed profile simultaneously, but none of these satisfy both the neutrino flux data, including GALLEX and SAGE, and the helioseismically determined density profile.Comment: 12 pages, 17 figures, uses pasj00.cls. Accepted for publication in PAS

Pulsations of Pre-White Dwarfs with Hydrogen-dominated Atmospheres

We carried out a fully non-adiabatic analysis for nonradial oscillations of pre-white dwarfs evolved from the post-Asymptotic Giant Branch (AGB) with hydrogen-dominated envelopes. It is shown that nuclear reactions in the hydrogen burning-shell excite low-degree g-modes in the period range of about 40-200 s for the pre-white dwarf models with Teff=40,000 K - 300,000 K. It is also shown that the amount of hydrogen {has} a significant influence on the instability domain of such pre-white dwarfs in the Hertzsprung-Russel (H-R) diagram. Thus, the thickness of hydrogen-dominated envelopes may be well constrained by observing the presence of the g-mode oscillations.Comment: PASJ accepted, 7 pages, 6 figure

Super-Nyquist Asteroseismology with Future Space Missions

We propose a photometric technique for future space missions that overcomes the problem of Nyquist aliases. These aliases result from typically long cadences of observation imposed by telemetry constraints. The proposed method is to introduce a periodic modulation to the sampling rate. Suitable combinations of the frequency and the amplitude of this modulation allow the true peaks to be distinguished from the aliases. We provide an analytical proof of the validity of this method and some demonstrations with simulated data. We also propose to divide a long cadence into two unequal parts, aiming at reproducing the intrinsic amplitude spectrum of stars without a severe smearing effect due to long exposures. The two exposures can be summed to recover the photon statistics if the user is interested in doing so. Based on these proposals, a specific recommendation for the PLATO mission is made to maximise its capability of photometry for asteroseismology, without serious interference with its other scientific missions.Comment: 13 pages, fig11a was replaced with the correct one. Proceedings of the PHOST "Physics of Oscillating Stars" conference (2-7 Sept. 2018, Banyuls-sur-mer, France), Edited by J. Ballot, S. Vauclair, & G. Vauclai

Deriving the orbital properties of pulsators in binary systems through their light arrival time delays

We present the latest developments to the phase modulation method for finding binaries among pulsating stars. We demonstrate how the orbital elements of a pulsating binary star can be obtained analytically, that is, without converting time delays to radial velocities by numerical differentiation. Using the time delays directly offers greater precision, and allows the parameters of much smaller orbits to be derived. The method is applied to KIC9651065, KIC10990452, and KIC8264492, and a set of the orbital parameters is obtained for each system. Radial velocity curves for these stars are deduced from the orbital elements thus obtained.Comment: 12 pages, 26 figures, 8 tables, accepted for publication in MNRA

FM stars: A Fourier view of pulsating binary stars, a new technique for measuring radial velocities photometrically

Some pulsating stars are good clocks. When they are found in binary stars, the frequencies of their luminosity variations are modulated by the Doppler effect caused by orbital motion. For each pulsation frequency this manifests itself as a multiplet separated by the orbital frequency in the Fourier transform of the light curve of the star. We derive the theoretical relations to exploit data from the Fourier transform to derive all the parameters of a binary system traditionally extracted from spectroscopic radial velocities, including the mass function which is easily derived from the amplitude ratio of the first orbital sidelobes to the central frequency for each pulsation frequency. This is a new technique that yields radial velocities from the Doppler shift of a pulsation frequency, thus eliminates the need to obtain spectra. For binary stars with pulsating components, an orbital solution can be obtained from the light curve alone. We give a complete derivation of this and demonstrate it both with artificial data, and with a case of a hierarchical eclipsing binary with {\it Kepler} mission data, KIC 4150611 (HD 181469). We show that it is possible to detect Jupiter-mass planets orbiting $\delta$ Sct and other pulsating stars with our technique. We also show how to distinguish orbital frequency multiplets from potentially similar nonradial $m$-mode multiplets and from oblique pulsation multiplets.Comment: 15 pages, 14 figures, accepted for publication in MNRA

Numerical simulations of line-profile variation beyond a single-surface approximation for oscillations in roAp stars

Prior to the last decade, most observations of roAp stars have concerned the light variations. Recently some new, striking results of spectroscopic observations with high time resolution, high spectral dispersion, and a high signal-to-noise ratio became available. Since the oscillations found in roAp stars are high overtones, the vertical wavelengths of the oscillations are so short that the amplitude and phase of the variation of each spectroscopic line are highly dependent on the level of the line profile. Hence, analyses of the variation of the spectroscopic lines of roAp stars potentially provide us with new information about the vertical structure of the atmosphere of these stars. In order to extract such information, a numerical simulation of the line-profile variation beyond a single-surface approximation is necessary. We carried out a numerical simulation of line-profile variation by taking account of the finite thickness of the line forming layer. We demonstrated how effective this treatment is, by comparing the simulation with the observed line profiles.Comment: PASJ, 64, 9 (2012), in press. 18 pages, 16 figure